X-ray tomography apparatus

ABSTRACT

Accordingly, the present invention provides an x-ray tomography apparatus having a patient table, x-ray tomography components located around the patient table and in an imaginary plane which intersects the table, and structure for supporting the table and tomography components and including apparatus for moving the tomography components along at least a portion of the table. In an alternate embodiment, an x-ray tomography apparatus includes an annular x-ray tomography system for continuously rotating around a patient, which structure has an electrically powered x-ray source and battery power for supplying electrical power to the x-ray source.

.Iadd.This application is a reissue application for U.S. Pat. No.4,928,283, based on U.S. Ser. No. 160,657, filed Feb. 26, 1988 byBernard M. Gordon. .Iaddend.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to x-ray tomography apparatusesand, in particular, to those apparatuses which are adapted for CAT scanoperations.

2. Statement of the Prior Art

CAT scans (computerized axial tomography) have been used for many years.Generally the system operates by taking multiple, cross-sectional, slicex-rays from different angles within a single plane passing through thebody. The results are mathematically compiled to create across-sectional image of the body in that plane. To produce these x-raysin one form, an x-ray source and an array of detectors are placed onopposite sides of an annular yoke, which yoke is made to rotate withinthe selected plane and around the patient.

An important consideration in scanning has been the accurate andconsistent alignment of the tomography components and the patient boththroughout the rotation and over the course of many scans and patients.Misalignment or movement can negatively influence the data of an entirescan. In order to deal with this factor, manufacturers of CAT scanapparatuses have typically produced a very large and massive machinewhich includes a heavy yoke for mounting the tomography components. Thehandling of this weight requires additional mass in the remainder of theapparatus and typically a large apparatus.

One ramification of the extra size and mass of these machines has beenthe requirement of a patient handling apparatus, as the weight of thepatient is typically much less than the weight of the yoke and otherrotating components. Thus, a moveable patient table has been used toproperly position the patient in the desired location relative to thefixed yoke, and this further contributes to the size and weight of theapparatus.

A further contibutor to the size and mass of these machines has been theproblem of delivering electrical power for the x-ray source to therotating apparatus. The two approaches primarily used have beenelectrical brushes, or slip rings, which constantly sweep duringrotation and extended cables which limit the rotation of the yoke toapproximately one revolution. Unfortunately, the brush approach createsa disruptive amount of electrical interference in the very sensitiveoutput signals of the detectors. Some of this interference can bereduced by the use of shielding; however, the shielding must beextensive as the brushes rotate around the entire large circumference ofthe yoke. The shielding also adds bulk and weight. More accuratemachines use the extended cables which limit rotation. Unfortunately,this approach requires much larger motors and produces greater systemstresses and wear, because the yoke and all of the of the moving massmust be accelerated and decelerated quickly in order to adequatelyoperate within the limited rotational range of the yoke.

The apparatus which results from these various requirements is large,heavy, expensive and one which is difficult to relocate. It requires alarge amount of floor space and thus cannot be used in space limitedenvironments. A further disadvantage caused by the size and weight ofthese apparatuses is the wear experienced in the moving parts thereof.

In another form of tomography apparatus known in the prior art, thex-ray source and an array of detectors are mounted on a "C" shaped framewhich is typically cantilevered and manipulated over the patient.Although this apparatus can be manipulated over a wide range, it alsorequires large amounts of space and mass for the manipulation apparatus.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a tomography apparatus whichhas a substantially reduced size and mass for enabling a high degree ofmobility for the apparatus while requiring a much smaller amount ofspace for the installation. An x-ray tomography apparatus provides apatient table means, x-ray tomography means located around the patienttable means and in an imaginary plane which intersects the table means,and means for supporting the table means and tomography means andincluding means for moving the tomography means along at least a portionof the table means. In an alternate embodiment, an x-ray tomographyapparatus includes an annular x-ray tomography means for continuouslyrotating around a patient, which means has an electrically powered x-raysource and battery powered means for supplying electrical power to thex-ray source.

The various tomography means of the present invention may be combinedwith several optional features which further enhance the size, weight,cost and independent movement of the tomography means both rotativelyaround the patient and otherwise. These optional features includes meansfor determining the relative position between the patient table meansand the tomography means to allow alignment error to be calculated intothe data compilation, a non-uniform detector configuration to reduce thenumber of detector channels used, and means for providing wirelesstransmission of the tomography data.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustratively described with respect to theaccompanying drawings in which:

FIG. 1 is a perspective view of an x-ray tomography apparatusconstructed in accordance with one embodiment of the present invention;

FIG. 2 is a perspective view of a different orientation of the apparatusof FIG. 1;

FIG. 3 is a sectional view of the apparatus of FIG. 1 taken along viewlines 2--2; and

FIG. 4 is a side view of an alternative embodiment of a portion of theapparatus of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an x-ray tomography apparatus 10 generally including apatient table 12, a tomography apparatus 14, and a support structure 16for the table 12 and the tomography apparatus 14. The patient table 12is intended to be removable from the support structure 16. Supportstructure 16 may take any suitable form capable of performing thefunctions described herein. As shown, structure 16 includes fourvertical support members or legs 18 connected to a floor bracket 19including side members 20 and end members 22.

Also included in the support structure 16 is a cradle 24 for supportingthe tomography means 14. Cradle 24 includes a lower cradle member 26 andan upper cradle member 28. Lower cradle member 26 is supported at eachend thereof by the side members 20 of the support structure 16. Thissupport is provided through bearing surfaces 30 to allow the supportmeans 24 and the tomography means 14 to be moved at least a portion ofthe length of the patient table 12. To effect this movement, a drivemeans 32 is coupled between end members 22 and engages the lower cradlemember 26. Drive means 32 may comprise any means capable of moving thecradle and tomography means 14 the required distances. One suitablemeans would be a worm gear engaging a portion of the lower cradle member26. Another would be a drive belt. In a preferred embodiment the drivemeans 32 is adapted to move the tomography means the entire length ofthe table 12. This would allow the apparatus to be used in an operatingroom setting where the tomography means 14 would be stored at a patientsfeet when not in use and thus not be in the way of surgeons or theanesthetist.

Cradle 24 is constructed with upper member 28 rotatably mounted to lowermember 26 to enable upper member 28, and therefore the tomography means14, to be rotated to a position parallel with the length of the table asshown in FIG. 2, for enabling easier transportation of the apparatus 10.To further this function, a pair of removable support blocks 34 aremounted on drive means 32 to steady the tomography apparatus in thetransport position. Also, the legs 18 may be stiffened by diagonalmembers (not shown) affixed to the end members 22, and wheels may alsobe mounted to the floor bracket 19. During transport the table 12 wouldbe removed from the support 16 and the tomography means 14 would beturned to the position shown in FIG. 2 which is substantially parallelto the length of the support 16.

FIG. 1 also shows means 33 for determining the position of thetomography means 14 with respect to the table 12. This function may beperformed by an suitable means such as some form of optical measurementsystem. The system may be mounted on the tomography means 14 at 33 asshown in FIG. 1 and make reference to the table 12, or it may be mountedon the table 12 and make reference to the tomography means 14. Specialmeasurement markings or indicia may also be mounted on either thetomography means 14 or table 12 for reference to by the system. Themeasurement system could provide information on both the angularposition of the tomography means 14 and any misalignment thereof withinthe rotational plane. All of this information can be used in compilingimages from the scan data. Thusly, misalignments during the scan couldbe used to provide more scan data for the construction of images becausethey would reduce the amount of duplicate data collected during thescan.

FIG. 3 is a sectional view of the apparatus of FIG. 1 taken along viewlines 3--3 and showing greater detail of the tomography means 14.Whereas the tomography means 14 may have various covers affixed theretofor providing a more esthetic apparatus, the would be covers are removedin FIG. 3 to allow a representational showing of the instrumentation.Tomography means 14 is shown to include a number of tomographycomponents including an x-ray source 40, an array of detectors 42, acontrol and data handling electronics package 44, a source of power forthe x-ray source 40 including batteries 46 and a power converter 47, anda source of power for the electronics package 44 including batteries 48and a power converter 49. It is anticipated that the tomogrphy means 14will have a patient opening or inner diameter of approximately 65 to 70centimeters and an outer diameter of approximately 125 to 140centimeters.

X-ray source 40 provides for the electrical generation of x-rays bymethods well known in the art. In a preferred embodiment the x-raysource 40 is adapted for continuous operation during a scanningoperation. This technique of scanning is referred to as Continuous WaveFan Beam Tomography and is described in greater detail in U.S. Pat. No.4,547,893, assigned to Analogic Corporation of Peabody, Mass. Thistechnique reduces the signal processing electronics necessary withattendant cost and weight savings. X-ray source 40 would also include acollimator for determining the x-ray fan beam and means for dissipatingexcess heat generated in the production of the x-rays.

The electronics package 44 provides for data handling from the detectors42 and for control of the x-ray process. This control is provided via atwo-way communication link between the electronics package 44 and acomputer 50 used for image processing and control. This two-waycommunication link may be achieved by any suitable means. Further, thecontrol and image processing methods which may be used by computer 50are well known in the CAT scanning art.

Power for the x-ray source 40 and for the data handling electronicspackage 44 is provided from the batteries 46 and 48 and the powerconverters 47 and 49, respectively. These power converters 47, 49provide the voltages necessary for the respective equipment which theypower. Power converter 47 is a high-voltage supply and power converter49 is a low voltage supply. Whenever the tomography means 14 is broughtto the rest position in between scans, shown in FIG. 3, a pair ofelectrical contacts 52 may be used to recharge the batteries 46 and 48in order to allow pseudo-continuous operation of the CAT scan. Thesecontacts 52 are shown to be connected to the batteries 46 and 48 viaelectrical lines 54. Converters 47, 49 would also include means fordissipating excess heat generated in the conversion process.

The detector array 42 includes three sections of detectors 56 and 58.The section 56 is located about a center line 60 which passes throughthe x-ray source 40 and through the center of rotation 62 of thetomography means 14. The section 56 of detectors is substantiallycentered on either side of the center line 60, with perhaps a smalloffset to avoid symetry about the center line 60 for providing greateramounts of collected data. The x-rays which strike the detectors withinsection 56 radiate along the radial lines located between radial lines64 and 66 passing from the x-ray source 40 to the detector array 42. Theother sections 58 of detectors are located adjacent to the section 56and are intended to receive x-ray information for x-rays radiatingbetween the radial lines 66 and 68, 64 and 70 from the source 40.Thusly, energy is only radiated from the source 40 within the fan beam72 located between radial lines 68 and 70.

The purpose of having two groups of detectors concerns the informationalcontent of the x-rays being detected. Within the radial lines 64 and 66are typically located all of the major organs and complex structure ofthe human body. The body structure located between radial lines 66 and68, 64 and 70 is typically much simpler and does not encompass vitalorgans. Therefore the informational content of the x-rays between lines64 and 66 is greater and more important than the informational contentof the x-rays between lines 66 and 68, 64 and 70. For this reason, it ispermissible to construct an array of detectors which has higher detectordensity in the section 56 and a lower detector density in the section58. This allows a reduction, and therefore a cost and weight savings, inthe number of detectors and the associated electronics used where theinformation to be collected simply is not present. In lieu of and/or incombination with varying detector densities, it may be desireable tosample the outer detectors 58 at a lower rate than the inner detectors56. It may also be desireable to have more than two groups of detectorshaving different detector densities and/or sampling rates. Thistechnique is discussed in greater detail in U.S. Pat. No. 4,677,554,also assigned to Analogic Corporation.

It should be noted that it is possible to construct the tomography means14 without having any detectors located to the left of section 56. Whenthe tomography means 14 is in the position shown in FIG. 3, data is notcollected for those portions of the body 74 which lie to the left ofradial line 64. Those portions 74 of the body are x-rayed as thetomography means 14 rotates through other angular positions with respectto the patient. Again, because this outer portion 74 contains no vitalorgans, the data to be collected therefrom is less significant and thestructure can be imaged by using less data collection. The eliminationof this additional section of detectors enables further weight and costsavings for the x-ray apparatus.

Also shown in FIG. 3 are means for rotatably supporting and for rotatingthe tomography means 14. Any suitable means may be used for thispurpose. Nominally shown in FIG. 3 are roller bearings 80 and a drivebelt apparatus 82. These means are capable of continuously rotating thetomography means 14 without stopping to collect data for individualscans. Continuous rotation enables the use of the Continuous Wave FanBeam Tomography technique referred to above. Continuous rotation ispossible because the tomography means is designed and constructed to beelectrically independent. It is anticipated that the tomography means 14will rotate at a speed of approximately one revolution every 4 to 5seconds or 12 to 15 revolutions per minute.

FIG. 4 shows an alternate embodiment 90 of tomography means 14 with theaddition of a circular frame or track 92 which is stationary andsurrounds the tomography components. The tomography components are bothconnected and held apart by a multiplicity of hollow separators 94through which electrical cables are run. The separators 94 are used tophysically bias the component apart and thus outwardly against the track92. The components engage the track 92 by means of wheels 96. The track92 thereby helps to provide rigidity to the tomography means 90.

Further disclosed in FIG. 4 as one of the tomography components is ameans 98 for rotating the tomography means 90 within the circular track92. This means 98 is an electrically powered locomotive means whichmight be powered by its own internal battery or any other suitablemeans. Locomotive means 98 engages the track 92 by any suitable meanssuch as a gear-and-tooth arrangement, and similar to the tomographymeans of FIG. 3, enables continuous rotation thereof. The remainder ofthe components of tomography means 90 of FIG. 3 are identical to thoseof the tomography means 14 of FIG. 3.

Also included as part of the structure of the tomography means 14 are apair of triangularly placed support members 100 and 102. The upper endsof members 100 and 102 are coupled to the x-ray source 40, preferably ata single coupling point (not shown. The lower ends of members 100 and102 are connected to opposite ends of the detector array 42. Thedetector array 42 is mounted on a rigid structure so that the endsthereof do not move with respect to one another. The distances betweenthe ends of the detector array 42 and the x-ray source describe atriangle which may either be equilateral or have an angle greater than60 degrees at the corner of x-ray source 40. The equilateral trianglewould provide the most clearance for the patient and table 12 if thesides of the triangle were straight. Because the detector array 42 isarcuate a non-equilateral triangle may be used. Thus, the members 100and 102 and detector array 42 form a pseudo-triangular structure forsignificantly enhancing nthe rigidity of the tomography means 90. Thisarrangement helps to provide both the proper alignment between the x-raysource 40 and the detector array 42 and also lends significant rigidityto the annular shape of the tomography means 90 which might otherwise bedistorted during rotation.

METHOD OF OPERATION

During scanning of a patient, the apparatus of the present invention maybe operated in any one of several modes. The most typical mode ofoperation would be to locate the tomography means 14 along the patienttable 12 by use of the drive means 32 at the desired position withrespect to a patient located on the table 12. This may be accomplishedby visual reference to the patient. When the tomography means 14 isproperly located, it is rotated to perform a set of scans in accordancewith the continuous wave tomography method. Signals to perform this scanare transmitted from the computer 50 to the electronics package 44,which then takes control of the operation.

The present apparatus may also be used to produce a simple x-ray of apatient in what may be termed a scout mode. To accomplish this, thetomography apparatus 14 is not rotated but moved along the table 12while the x-raying is performed. The data collected from this operationis used to produce a normal x-ray of the patient, such as that whichmight be used to determine the general location of specific organs andother points. As the fan beam of x-rays shown in FIG. 3 does not coverthe entire patient, and in particular the portion 74, it would simply benecessary to rotate tomography means 14 until the width of the fan beamat the center of rotation 62 were sufficient to encompass the entirebody prior to performing the scout scan of the patient. Such simplex-rays may also be effected by scanning the patient twice, first withthe position of the tomography means shown in FIG. 3, and then againwith the tomography means 14 inverted to cover the portion 78 of thepatient. This method would produce an enchanced image for the areacovered by detector section 56.

Lastly, it is possible to perform a helical scan of the patient bysimultaneously rotating the tomography means 14 and moving it along thepatient table 12. This scanning method allows three dimensional data tobe collected, from which data it would be mathematically possible toconstruct an image for any slice through the scanned volume. Thus apatent's head could be scanned as a volume and the radiologist wouldhave available any image of the head that he or she might want. Thiswould avoid the necessity of bringing a patient back for additionalx-rays when more information is desired.

The embodiments of the present invention described are intended to betaken in an illustrative and not a limiting sense. Various modificationsand changes may be made to these embodiments by persons skilled in theart without departing from the scope of the present invention as definedin the appended claims.

What is claimed is:
 1. An x-ray tomography apparatus, comprising:anelongated patient table means having opposite ends; a rotary fan beamx-ray tomography means encircling the patient table means; and means forsupporting the table means at opposite ends thereof and for supportingthe tomography means from underneath and including means for moving thetomography means along a substantial portion of the table means, whereinthe tomography means includes means for causing at least a portion ofthe tomography means to continuously rotate around the table means. 2.The apparatus of claim 1, wherein the tomography means comprises amultiplicity of members including an x-ray source, an array ofdetectors, tomography electronics and at least one means for supplyingelectrical power for the tomography means.
 3. The apparatus of claim 2,further comprising means for physically interconnecting the members ofthe tomography means in an annular shape for rotation around the tablemeans.
 4. The apparatus of claim 3, wherein the tomography means furtherincludes triangularly placed structural members affixed between thex-ray source and the array of detectors.
 5. The apparatus of claim 4,wherein the array of detectors includes a support member which extendsbetween the triangularly placed structural members.
 6. The apparatus ofclaim 2, further comprising means for transmitting control and datasignals to and from the tomography means.
 7. The apparatus of claim 2,wherein the means for supplying electrical power are battery powered. 8.The apparatus of claim 2, wherein the rotation of the tomography meansdefines a center of rotation thereof and further wherein the array ofdetectors includes at least first and second groups of detectors withthe first group being substantially centered about an imaginary linepassing through the x-ray source and the center of rotation and thesecond group being located adjacently to the first group.
 9. Theapparatus of claim 8, wherein the first group of detectors has a higheraverage detector density than the second group.
 10. The apparatus ofclaim 1, further comprising means for determining the relative positionbetween the tomography means and the patient table means.
 11. Theapparatus of claim 1, wherein the means for supporting is elongated andthe table means is removable from the means for supporting, and furtherwherein the means for supporting includes means for allowing orientationof the tomography means to a position where an imaginary plane ofrotation defined by the rotating portion of the tomography means issubstantially parallel with the elongated means for supporting. .Iadd.12. An X-ray tomography apparatus comprising in combination: a supportstructure for supporting an elongated patient table; tomographicscanning means also supported on said support structure, said scanningmeans including an X-ray source and X-ray detection means for detectingX-rays emitted by said X-ray source; means for rotating said scanningmeans about a rotation axis so as to circumscribe an inner region largeenough to encompass said patient table with a patient thereon; and,means for pivoting said scanning means between a first position whereinsaid scanning means is rotatable so as to define a scanning planesubstantially normal to the elongated direction of said table, and asecond position wherein said plane is substantially parallel to saidelongated direction. .Iaddend. .Iadd.13. The apparatus of claim 12further comprising means for supporting said scanning means for linearmovement along a path substantially parallel to the elongated directionof said patient table. .Iaddend. .Iadd.14. The apparatus of claim 13further comprising means for supporting said patient table so that thelatter extends through said inner region when said scanning means is insaid first position, said means for supporting including a base andmeans coupled to said base for removably supporting said patient tablethereon, said scanning means being mounted on said base so that whensaid patient table is removed, said scanning means is pivotable withrespect to said base between said first and second positions withouthindrance from said table or means for supporting said table. .Iaddend..Iadd.15. The apparatus of claim 14, wherein said scanning means ispivotable about said base so that the orientation of said scanning planecan be varied with respect to the elongated direction of said table..Iaddend. .Iadd.16. The apparatus of claim 15 further comprising meansfor determining the relative alignment of said scanning plane with saidtable. .Iaddend. .Iadd.17. The apparatus of claim 12, further comprisesmeans for physically interconnecting the members of the tomographyscanning means in an annular shape for rotation around the table..Iaddend. .Iadd.18. The apparatus of claim 12 further comprising batterymeans for powering said apparatus. .Iaddend. .Iadd.19. The apparatus ofclaim 18 wherein said battery means comprise rechargeable batteries..Iaddend. .Iadd.20. An X-ray tomography apparatus comprising incombination:(a) x-ray tomography means disposed in an annularconfiguration so as to define a scanning region large enough toaccommodate a patient and a movable patient table; (b) patient tablesupport means for supporting a movable patient table having a head endand a foot end within said scanning region, said patient table supportmeans comprising a support structure and at least one vertical supportmember; (c) tomography support means supported by said support structurefor supporting said tomography means for linear movement along an axisrunning between the head end and the foot end of said patient table andfor pivoting said tomography means between a first position wherein theplane of said annular configuration is substantially normal to said axisand a second position wherein the plane is substantially parallel tosaid axis; and (d) tomography rotation means for orbital movement ofsaid tomography means around said scanning region. .Iaddend. .Iadd.21.The apparatus of claim 20 further comprising battery means for poweringsaid apparatus. .Iaddend. .Iadd.22. The apparatus of claim 21 whereinsaid battery means comprise rechargeable batteries. .Iaddend. .Iadd.23.The apparatus of claim 20 wherein said patient table support meanscomprise a plurality of vertical support members attached to saidsupport structure at their lower ends and adapted to support saidpatient table at their upper ends. .Iaddend. .Iadd.24. The apparatus ofclaim 23 wherein said support members define an open, box-like regionfor at least partially accommodating said tomography means when it is insaid second position. .Iaddend.